Fuel burners built consistent with the Babington atomization principle are well known. The methodology mimics the atomization of water over a blowhole of a whale when the whale exhales. In the burner, a thin layer of fuel is poured over a convex surface that has a tiny air hole. Pressurized clean air is forced through the hole, creating a spray so fine that when burned, it creates no smoke, odor or carbon monoxide. By way of non-limiting example, the AIRTRONIC series of burners by BABINGTON TECHNOLOGY operate on this principle. Non-limiting examples of patents that disclose burners built according to this principle include, e.g., U.S. Pat. No. 4,298,338 entitled LIQUID FUEL BURNERS, U.S. Pat. No. 4,507,076 entitled ATOMIZATION APPARATUS AND METHOD FOR LIQUID FUEL BURNERS AND LIQUID ATOMIZERS, or U.S. Pat. No. 8,622,737 entitled PERFORATED FLAME TUBE FOR A LIQUID FUEL BURNER, the contents of which are incorporated herein by reference in their entireties, may be used.
Referring to FIG. 11, an exploded view of the AIRTRONIC burner 1100 is shown. The burner includes a double shafted AC motor 1102 with a fixed speed. AC motor 1102 collectively drives a fuel pump 1104, an atomizing air compressor 1106, and a combustion air blower 1108. Fuel pump 1104 delivers a stream of fuel from a reservoir 1110 to a point above convex heads (not shown) of an atomizing chamber 1111. Air compressor 1106 injects air through a small hole in the heads spraying fuel as it flows over the hole of heads and projects the atomized fuel into flame tube 1116 (a process known as “atomization,” thus air compressor 1106 being an “atomizing” air compressor). An ignitor (not shown) ignites the atomized fuel. Combustion air blower 1108 delivers a flow of air to the flame tube 1116 that combusts with the fuel to provide flame and heat, and to carry the heat and combusting fuel out of the flame tube 1116.
In an atomization burner the flow of compressed air, combustion air and fuel must maintain a certain mixture relationship in order to properly combust the fuel. For example, a particular flow of atomizing air can only function with a certain range of fuel flow. Fuel flow in excess of that range is too thick to properly atomize, while fuel flow below that range is so thin that particles are too small to properly combust. Fuel flow above or below that range simply will not combust and/or will sub-optimally combust and generate byproducts (e.g., smoke, odor).
By nature of its design, the AIRTRONIC has constrained flexibility relative to this relationship. The fixed speed of the single AC motor 1102 drives fuel pump 1104, combustion air blower 1108, and atomizing air compressor 1106 at corresponding fixed maximum speeds. The flow of air from the compressor 1106 to atomizer heads (not shown) is not adjustable, which limits the potential range of fuel flow rate as noted above. The flow rate of fuel from fuel pump 1104 has some flexibility to reduce the fuel flow via an adjustable mechanical restrictor in the fuel flow pathway, but this is only accessible at the point of manufacture and is not adjustable by the consumer (absent disassembly). The flow of combustion air has some greater degree of flexibility, and is manually adjustable via a knob 1109 to physically restrict the air pathway from combustion air blower 1108 to flame tube 116. This design combust fuel at a rate of 0.45-0.55 gallons per hour (“GPH”), although approximately 0.4-0.6 GPH is the theoretical range limit.
In recent years a market has emerged for portable cooking and heating appliances to cook for significant numbers of people at locations that do not have access to working kitchen facilities. For example, disaster relief operations need transportable kitchen appliances to bring to disaster zones and relief centers. Military units need kitchen appliances to support operations as personnel are deployed and relocate base camp. Restaurants and caterers may wish to cook at remote locations, such as beaches, wooded areas, street fairs, etc. A need therefore exists for portable and/or mobile kitchen appliances.
A difficulty with portable and/or mobile kitchen appliances is that it can be difficult to obtain different types of fuel in such circumstances as well as operate on reliable and sufficient electrical power. For example, if the transporting vehicle runs on gasoline and the cooking appliances run off propane, then there is a need to store, transport and maintain a supply of two different fuels. Gasoline and propane are also volatile fuels and dangerous to transport and store in the field. Organizations that provide such services therefore prefer that kitchen appliances and the vehicles that transport them consume the same type of fuel. Liquid distillate fuel, such as diesel as burned by the AIRTRONIC, is preferred. Applicants have several patents and applications to utilize a burner such as the AIRTRONIC in connection with portable cooking appliances, such as U.S. Pat. No. 8,499,755 entitled MOBILE KITCHEN, U.S. Pat. No. 7,798,138 entitled CONVECTION OVEN INDIRECTLY HEATED BY A FUEL BURNER, the contents of which are incorporated by reference herein in their entireties.
Use of the AIRTRONIC with portable cooking and/or heating appliances has a variety of drawbacks.
One drawback is that even at its minimal fuel flow rate the AIRTRONIC produces more heat than necessary for particular cooking apparatus. Some cooking appliances need to be overbuilt to withstand this heat output, which makes the appliance expensive to manufacture, heavy and energy inefficient. By way of non-limiting example, an oven as shown in U.S. Pat. No. 7,798,138 that could withstand the heat output of the AIRTRONIC weighs on the order of 800 lbs., which limits its portability options.
It is also difficult to change the temperature of the appliance. The overbuilt nature of the appliance needed to withstand the excessive heat output has a corresponding large specific heat, which makes the appliance slow to heat (wasting time and fuel) and slow to cool (potentially overcooking food). By way of non-limiting example, a chef may want to instantaneously reduce a stockpot cooker from a HIGH setting (e.g., to boil) to LOW setting (e.g., to simmer), but this takes several minutes even if the burner is turned off because the stockpot cooker itself has a high specific heat that retains the original high heat from the HIGH setting and only slowly cools.
It is also difficult to control the appliance temperature. The AIRTRONIC controls heat output via the “bang-bang” methodology, in that it is turned ON or OFF as appropriate to reach/maintain a desired temperature, also known as duty cycling. However, the AIRTRONIC takes 20-30 seconds to turn ON, and 90-120 seconds to turn OFF. By way of non-limiting example, in an oven preheated to 400 degrees, even if the burner is turned OFF when the oven reaches 400 degrees the burner continues to output heat. The oven will thus overshoot its preheat target to a higher temperature, and the specific heat of the appliance will slow the transition from the higher temperature to the desired preheat temperature.
The AIRTRONIC also consumes a considerable amount of power to operate because when active the components are at maximum flow speeds. Any adjustment in flow rates as noted above is due to physical impediments from restrictors in the flow pathways which can reduce flow but do not reduce power consumption. This level of power consumption is undesirable given the limited availability of power in the environments that would utilize portable cooking appliances.